OFDMA and single carrier FDMA have been selected as the downlink and uplink multiple access schemes for the E-UTRA air interface currently been studied in 3GPP (which is a standard based collaboration looking at the future evolution of third generation mobile telecommunication systems). Under the E-UTRA system, a base station which communicates with a number of user devices allocates the total amount of time/frequency resource (depending on bandwidth) among as many simultaneous users as possible, in order to enable efficient and fast link adaptation and to attain maximum multi-user diversity gain. The resource allocated to each user device is based on the instantaneous channel conditions between the user device and the base station and is informed through a control channel monitored by the user device.
When data is transmitted from the user device to the base station, an acknowledgment (ACK) or a non-acknowledgment (NACK) is typically signalled back from the base station to the user device. Under the current proposals for E-UTRA, these ACK/NACK messages are to be sent in the downlink control channel for the user device. However, the inventor has realised that this leads to a problem that the size of the control channel will vary depending on the situation of the user device.